Frogs' habitats affected

Climate change and global warming caused by greenhouse gas emissions have important implications on re-shaping Earth’s landscape. Animal species can suffer dramatic consequences, possibly even extinction, from these changes.

Scientists have been studying how climate change affects the habitat of frogs, and in what ways changes to their habitat conditions could lead to the risk of extinction of some species and the consequent loss of biodiversity amongst the amphibians.

In the study, scientists from the University of Evora in Portugal and the Brown University in Rhode Island, US, used a model that attempts to predict the geographical movements of 15 different species of amphibians in the western coast of US up to the year 2100, under two different greenhouse gas emission scenarios – one moderate and one more extreme. The models, based on weather data of the same region between 1961 and 1990, analysed the geographical distribution of the different species and predicted for each of them the possible range of movements (technically defined as “shifts”) that the species could undergo because of the modifications to climate conditions.

In their work, published this year in the international journal Ecology Letters, Regan Early and Dov F. Sax observed that there can be discontinuities in the path of frogs’ movements. These discontinuities are called gaps and consist of particularly hostile geographical regions that block the migration from one place, whose climate becomes hostile for the survival of the species, to another place where a more suitable climate exists. These regions could be physical barriers such as mountains. “For example, [one frog species] may be unable to shift into its full potential future range because climate variability after 2050 causes the landscape connecting northern California and Southern Oregon to become climatically suitable only transiently”, explain the scientists. In simple words, if the species wants to move it should do it very quickly, otherwise the region will be not accessible anymore and a gap will block future movements. Scientists claimed that gaps in the climate-path or range shifts of a species could seriously endanger its survival in the long term up to 2100.

But not all hope is lost for the frogs. The scientists discovered two factors that can determine the ability of the frogs to emigrate to places with more suitable climatic conditions, in either greenhouse emission scenario: spreading the population in a certain territory (defined as dispersal), and the frog’s ability to persist in a certain geographic area for a short time, even in non favourable climatic conditions (called persistence). The better the species is at these two things, the better their chances of survival will be. The most surprising discovery was that particularly persistence ability up to one decade would be the most favourable factor to expand the range shift of a species in a scenario where local climate fluctuations and variability occur.

Other scientists have argued some limitations of the study, in particular regarding the assumption that the species’ distribution is in equilibrium with its environment, and the assumption that species cannot live in the future in climatic conditions which are different from those they are used to live. For instance scientists suggested that in the Pleistocene (from 2,588,000 to 11,700 years ago) some amphibians could live under climatic conditions that were very different from those in which they live nowadays.

Although adaptation of the species is a further important factor to be investigated, the present study gives some guidelines which may be useful in order to conserve the biodiversity of species. For example, we could promote movements along certain territories by assisting or increasing populations that naturally establish themselves in the territories or mitigating the impacts of climate changes using irrigations to improve habitat quality. In the case when gaps are present in the climate-path, we could even consider whether to use or not the controversial strategy of “managed relocation” or assisted migration of some species into more suitable habitats.

“Further refinement and application of climate-path analysis […] would improve our ability to forecast species’ responses to climate change and inform our use of alternative conservation strategies”, comment the two scientists in their work. In other words, if we can understand where they would like to move, we could help them do it.